Abstract: In this paper, the effect of Cu single atom modification on the adsorption of CO and electronic properties of Fe (111) surface has been studied by density functional theory (DFT). Two ways of adsorption and substitution have been studied for Cu mono-atom modification. The results show that the adsorption capacity of CO on the Cu modified Fe (111) becomes weak. One reason is that the sites provided by the Cu atom itself are weak for CO, and the other is that Cu weakens the adsorption of CO on the Fe nearby Cu. The analysis of electronic properties indicates that when Cu acts on the Fe (111), the part electrons of Fe can be transferred to the Cu, which weakens the electronic interaction between Fe and adsorbed molecules, and adjusts its adsorption capacity. Therefore, the Fe surface modified by Cu atom can well adjust the adsorption, dissociation and subsequent reaction catalytic activity of CO, which provides basic information to further explore the syngas catalytic reaction mechanism of Cu modified Fe surface.